Spectroscopic probes have been used in various fields because of their high sensitivity and great temporal and spatial sampling capability. The development of new spectroscopic probes with superior properties is important for the detection of different analytes.

Prof. MA Huimin. Dr. SHI Wen and their co-workers from CAS Key Laboratory of Analytical Chemistry for Living Biosystems have developed a series of new spectroscopic probes for bio-molecules (Chem. Commun. 2008, 1856-1858; Chem. Commun. 2010, 46, 2560-2562; Chem. Commun. 2011, 47, 8638-8640; Chem. Eur. J. 2010, 16, 6638-6643; Chem. Eur. J. 2012, 18, 925-930) and published an invited Feature Article entitled “Spectroscopic probes with changeable π-conjugated system” in Chem. Commun. (2012, doi: 10.1039/ C2CC33366J).

Recently, the researchers designed a tunable ratiometric pH probe based on carbon nanodots. Cell imaging studies showed that the probe can be distributed in the whole cells instead of the specific organelles such as endosomes or lysosomes, which demonstrates its good biocompatibility and intracellular dispersibility. Quantitative determinations of intracellular pH of intact Hela cells and the pH fluctuations associated with oxidative stress have been successfully performed with the probe. Decrease of intracellular reduced glutathione (GSH) leads to the acidification of cells, but GSH above its normal level has no obvious effect. Moreover, elevated ClO^- does not decrease the intracellular pH as H₂O₂ does. These observations have revealed an interesting phenomenon that the disturbance of oxidative stress usually decreases rather than increases the intracellular pH (unidirectional change). In addition, the proposed pH probe may have a great potential for quantitatively monitoring the intracellular pH fluctuations under different stimuli.

This result has been published in Angew. Chem. Int. Ed. 2012, 51, 6432-6435. The research is supported by National Nature Science Foundation of China, Ministry of Science and Technology of China and the Chinese Academy of Sciences.

A tunable ratiometric pH sensor based on carbon nanodots (by SHI Wen and MA Huimin)